Pulsed-current has been used alone, and in combination with periodic-reverse current, to influence the microstructure and morphology of electrolytically plated bodies.
The time scales historically used for cathodic current pulses have been on the order of microseconds to deciseconds, although for commercial applications time scales of milliseconds have been more common. Where periodic-reverse current is applied, the time scale for the anodic pulses is similar to, or somewhat greater than, the time scale for the cathodic pulses.
There are also specific "off" times of zero current or reduced current associated with the "on" times. This gives rise to duty cycle values for the anodic and cathodic pulse waveform repeating units. Thus the variables of: cathodic pulse time, amplitude and duty cycle; anodic pulse time, amplitude and duty cycle; pulse shape; ratio of anodic to cathodic coulombs per repeating unit; and net mean current and current density all have a significant bearing on the operation and performance of the overall pulsed plating process.
For a specific set of other conditions, including material being plated, specific plating electrolyte, temperature, flow condition, etc., the electrical waveform variables must be optimized to optimize the process. Further, specific pulse time scales may affect specific dimension scales on the deposited surface, such that microscale roughness may be controlled but macroscale roughness is not controlled. Similarly, pulse time scales may also affect specific dimension scales on the deposited surface, such that macroscale roughness is controlled but microscale roughness is not controlled.
As a result of the foregoing considerations, the optimization of a pulsed-plating process is very complex, limiting its usefulness to platers in the general commercial world.
Examples of such electrolytic processes are disclosed in the following patents: U.S. Pat. Nos. 3,929,593 to Sugiyama et al., 3,969,195 to Dotzu, 3,975,254 to Felco et al., 4,140,596 to Wobking, 4,414,077 to Yoshida et al., 4,436,591 to de Hek, 4,517,059 to Loch et al., 4,545,875 to Riley, 4,666,567 to Loch, 4,704,196 to Saito et al., 5,202,018 to Haranyl et al., 5,242,556 to Masuzawa.
Although the concept of self-similar, i.e, fractal, topography has been studied and utilized, to date all uses of fractal concepts relate to analysis of signals and information processes, understanding of naturally occurring fractal structures and mathematical objects, and production of images for decorative purposes. Examples of the use of fractal topography are disclosed in the following publications: "Chaos", J. Gleick, Penguin Books (1987); "Exploring the Geometry of Nature", E. Rietman, Windcrest Books, Blue Ridge Summit, Pennsylvania (1989); "The Arrow of Time", P. Coveney and R.
Highfield, Ballantine Books, New York (1990); "Geometrical forms known as fractals find sense in chaos" Smithsonian, December 1983, pp. 110-117; "Fractal Analysis of Zinc Electrodeposition", J. Electrochem Soc., V. 137, No. 7, July 1990, pp. 2047-51; "Researchers Find Order, Beauty in Chaotic Chemical Systems", C&EN, Jan. 21, 1991, pp. 18-29; "Fractals offer Mathematical Tool for Study of Complex Chemical Systems", C&EN, Apr. 22, 1991, pp. 28-35; and "Beating a Fractal Drum" Science Dec. 13, 1991, p. 1593.
In view of the prior art, a need currently exists for a control variable having a fractal structure that can be utilized to optimize and improve a procedure or product. Additionally, a need exists for an electroforming process and apparatus providing great control over the deposition of an electrolytic material upon a substrate. The present invention provides such a process and apparatus.